1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to a device for controlling spreading of liquid crystal, which can maximize spreading of the liquid crystal in dropping the liquid crystal, and a method for fabricating an LCD.
2. Background of the Related Art
Keeping pace with development of an information oriented society, demands on displays increase gradually in a variety of forms, and, recently to meet the demands, different flat display panels, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), Vacuum Fluorescent Display (VFD), and the like, have been under development, and some of which are employed as displays in various apparatuses.
Of the different flat displays, the LCDs have been used most widely as mobile displays while the LCDs replaces the Cathode Ray Tube (CRT) owing to features and advantages of excellent picture quality, light weight, thin size, and low power consumption. Besides the mobile type LCDs, such as notebook computer monitors, the LCDs are under development for televisions (TVs) for receiving and displaying broadcasting signals, and computer monitors.
The LCD is provided with two opposite substrates, and liquid crystal injected between the two opposite substrates for varying a phase with temperature or density.
The liquid crystal is a substance having intermediate properties of liquid and solid, with a liquidity of a liquid and a long range order property of a solid. That is, the liquid crystal is a substance of an intermediate state of crystalline solid and liquid before a crystalline solid is melted into liquid. Upon directing light, or applying electricity, or magnetic field to the liquid crystal, a birefringence peculiar to an optical anisotropic crystal is shown, and within a certain temperature range, properties both of the liquid and the crystalline solid are shown.
The foregoing LCD is fabricated by progressing an array process, a cell process, and a module process on a glass substrate.
In the array process, wiring patterns, or switching devices (in a case of an active matrix type), such as thin film transistors (TFT), are fabricated. In the cell process, orientation processing, spacer disposal, or liquid crystal injection into the opposite glass substrates and sealing, are made. In the module process, a driver integrated circuit (IC), and a back light are fitted.
A liquid crystal injection process in the cell process will be briefly explained.
At first, a large sized panel is provided, which is formed by bonding and setting a first substrate inclusive of a plurality of TFT unit substrate regions, and a second substrate inclusive of a plurality of color filter unit substrate regions, by means of sealant.
The TFT unit substrate regions are provided with a plurality of gatelines running in one direction at fixed intervals, a plurality of datalines running in one direction perpendicular to the gatelines at fixed intervals, and a plurality of thin film transistors and pixel electrodes formed at a matrix of pixel regions defined by the gatelines and the datalines, which are formed in array process, respectively.
The color filter unit substrate regions are provided with a black matrix layer for shielding light from parts excluding the pixel region, the color filter layer, the common electrode, and the like.
The large sized panel is cut into a plurality of LCD unit panels. Then, liquid crystal and the plurality of LCD unit panels are placed in a vacuum chamber, and an injection hole formed by sealant is dipped in the liquid crystal. Then, by restoring the vacuum chamber to atmospheric pressure, the liquid crystal is injected between the LCD unit panel. This liquid crystal injection method is referred to as a vacuum injection method, which will be explained in more detail.
Referring to FIG. 1, liquid crystal is filled into a container 30, and placed in a chamber 20. Then, a deaeration process is carried out, in which the chamber 20 is maintained at a vacuum to remove moisture from an inside of the liquid crystal, or attached to an inside wall chamber, and fine air bubbles in the liquid crystal.
Next, after the liquid crystal injection holes of the LCD unit panels 40 are dipped, or brought into contact with the liquid crystal, nitrogen gas N2 is introduced into the chamber 20 to boost a pressure of the chamber from a vacuum to atmospheric pressure. Then, the liquid crystal is injected into the LCD unit panels through the injection holes by a pressure difference between a pressure inside of the LCD unit panels 40 and a pressure in the chamber.
When the liquid crystal 25 is filled in the LCD unit panels 40 fully, the LCD unit panels 40 are cleaned after the injection holes are sealed.
The foregoing liquid crystal injection method has a poor productivity because of the long time period required for the liquid crystal injection caused by cutting into LCD unit panels, maintaining a space between the two substrate at a vacuum, dipping the LCD unit substrates into the liquid crystal, or bringing the LCD unit substrates into contact with the liquid crystal. Moreover, when a large sized LCD is fabricated, since liquid crystal may not be injected into the LCD unit panel perfectly, this causes a defective LCD.
Eventually, for coping with the foregoing problem, the following liquid crystal dropping method has been recently suggested. A method for fabricating an LCD having the liquid crystal dropping method applied thereto will be explained, with reference to FIG. 2.
Referring to FIG. 2, orientation material is coated on a first substrate having TFT unit substrate regions, and a second substrate having color filter unit substrate regions. Then, an orientation process is conducted such that liquid crystal molecules have an orientation (1S), and the first, and the second substrates are cleaned (2S).
The cleaned second substrate is loaded on a seal dispenser, and sealant is coated to a periphery of each of the panel regions (3S). As the sealant, photo, or thermo setting resin is employed, and no liquid crystal injection hole is required.
On the other hand, the first substrate is loaded on a liquid crystal (LC) dispenser, and the liquid crystal is dropped on active array regions of respective panels (6S). In this instance, the cleaned first or second substrate may be loaded on a silver (Ag) dispenser, to form Ag dots on the common voltage supply line on the first substrate, or formation of the Ag dots may be omitted as in an In Plane Switching (IPS) mode.
The liquid crystal dropping method will be briefly explained.
Referring to FIG. 3, a first substrate 60 is loaded on a table 70 of a liquid crystal dispenser 50. There is a syringe 80 full of liquid crystal over the first substrate 60, for dropping liquid crystal thereon.
In general, the liquid crystal 65 is dropped in a form of a drop on the substrate 60. The substrate 60 moves at a fixed speed and direction, and the syringe 80 discharges the liquid crystal 65 matched thereto, thereby setting a liquid crystal dropping location.
Though not shown in the drawings, the syringe 80 has an external gas line connected thereto, for supplying nitrogen gas N2 from an external gas source, to apply a pressure to the liquid crystal, and drop the liquid crystal.
Next, referring to FIG. 2, the first and second substrates are loaded on a vacuum bonding chamber, and bonded such that the dropped liquid crystal is filled in the panel uniformly, and the sealant is set (7S), to complete fabrication of the large sized panel.
Then, an Scribe/Break (S/B) process (9S) is conducted, inclusive of a scribing process in which cutting lines are formed in a surface of glass by using a diamond pen, which has a hardness higher than glass, and a breaking process in which a force is applied to the glass, to break the glass, thereby cutting the large sized panel into of a plurality of LCD unit panels of unit cells.
Then, after subjecting surfaces of the LCD unit panel to grinding (10S), the LCD unit panels are subjected to Auto/Probe (A/P) inspection (11S), to finish a liquid crystal cell process.
In the A/P inspection, a device having a voltage terminal for applying a voltage is employed for examining electric defects of the LCD unit panel. That is, the voltage terminal is electrically connected to the gateline and dataline on the TFT substrate in the LCD unit panel, for examining cell gap defects or defective liquid crystal injection (imperfect injection, or leak) in the unit panel.
Though not shown in the drawing, upon finishing a liquid crystal cell fabrication process through the foregoing series of fabrication processes, a module fabrication process is performed, in which a driver IC, or back light is fitted.
However, the related art method for fabricating an LCD having the liquid crystal dropping method applied thereto has the following problems.
In the bonding process, the first and second substrates are aligned opposite to each other, and the environment is evacuated until the liquid crystal is spread on the surface of the substrate, and reaches to a section of the sealant in a periphery, thereby the two substrates are bonded.
In detail, referring to FIG. 4, liquid crystal is dropped on the first substrate 60 in forms of drops at fixed intervals. Distances between adjacent liquid crystal drops 65 have relations of d2=d4=d6=d8>d1=d3=d5=d7.
Next, referring to FIG. 5, the dropped liquid crystal 65 is spread slowly on the surface of the substrate in a circular form 65A during bonding the first and the second substrates together. Gaps 67, in which the liquid crystal is not yet filled, are formed before the liquid crystal is spread completely. Therefore, the environment is evacuated until the gaps 67 become adequately small, in the bonding of the first and second substrates.
However, it takes about 20 minutes until the gaps 67 become adequately small, enough to finish the liquid crystal spreading. There has been a hazard of peeling off of the sealant, and subsequent leakage of the liquid crystal, caused by a pressure difference between inside and outside of the substrates during such a waiting time period.
Though not shown, blots may occur at boundaries of the dropped liquid crystal, which deteriorates a picture quality.